There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e. without inserting a tube into the airway of the patient or surgically inserting a tracheal tube in their oesophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, which varies with the patient's respiratory cycle, to treat a medical disorder, such as sleep apnoea syndrome, in particular, obstructive sleep apnoea (OSA).
Non-invasive ventilation and pressure support therapies involve the placement of a patient interface comprising a mask component on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal pillow/cushion having nasal prongs that are received within the patient's nostrils, a nasal/oral mask that covers the nose and mouth, or a full face mask that covers the patient's face. The patient interface interfaces between the ventilator or pressure support device and the airway of the patient, so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient.
Such assemblies are typically maintained on the face of a patient by headgear having one or more straps adapted to fit over/around the patient's head.
FIG. 1 shows a typical system to provide respiratory therapy to a patient. This system will be referred to in the description and claims as a “patient interface assembly”.
The assembly 2 includes a pressure generating device 4, a delivery conduit 16 coupled to an elbow connector 18, and the patient interface 10. The pressure generating device 4 is structured to generate a flow of breathing gas and may include, without limitation, ventilators, constant pressure support devices (such as a continuous positive airway pressure device, or CPAP device), variable pressure devices, and auto-titration pressure support devices.
Delivery conduit 16 communicates the flow of breathing gas from pressure generating device 4 to patient interface 10 through the elbow connector 18. The delivery conduit 16, elbow connector 18 and patient interface 10 are often collectively referred to as a patient circuit.
The patient interface includes a patient interface element which is a mask 12 in the form of a shell 15 and cushion 14, which in the exemplary embodiment is a nasal and oral mask. However, any type of mask, such as a nasal-only mask, a nasal pillow/cushion or a full face mask, which facilitates the delivery of the flow of breathing gas to the airway of a patient, may be used as mask. The cushion 14 is made of a soft, flexible material, such as, without limitation, silicone, an appropriately soft thermoplastic elastomer, a closed cell foam, or any combination of such materials.
An opening in the shell 15, to which elbow connector 18 is coupled, allows the flow of breathing gas from pressure generating device 4 to be communicated to an interior space defined by the shell 15 and cushion 14, and then to the airway of a patient.
The patient interface assembly 10 also includes a headgear component 19, which in the illustrated embodiment is a two-point headgear. Headgear component 19 includes a first and a second strap 20, each of which is structured to be positioned on the side of the face of the patient above the patient's ear.
Headgear component 19 further includes a first and a second mask attachment element 22 to couple the end of one of the straps 20 to the respective side of mask 12.
A problem with this type of assembly is that the headgear force vectors necessary to achieve a robust and stable seal against the face of the patient can cut a straight line near the corners of a patient's eyes, which can be uncomfortable and distracting.
In order to avoid this, it is well known to include as part of the patient interface a forehead support to spread the required forces over a larger area. In this way, an additional cushion support on the forehead balances the forces put by the mask around the nose or nose and mouth.
All faces are different to each other. When using a patient interface assembly which has a forehead support, this forehead support should be adjustable for personal fit. The offset between facial plane and the forehead support can differ in the range of 30 mm. An example of known adjustment arrangement uses a rotating mechanism, controlled by a rotary knob. This mechanism results in an increase or decrease of the offset between the facial plane and the forehead support. The user has to rotate the knob to get the right offset and the right fit.
From an ergonomics perspective, rotating a knob is not the most convenient way to implement adjustment. The number of elements and required accuracy is costly and the assembly can be noise due to play between components.